Rotary expansible chamber devices – Unlike helical surfaces on relatively wobbling rotating...
Reexamination Certificate
1999-04-26
2001-05-08
Denion, Thomas (Department: 3748)
Rotary expansible chamber devices
Unlike helical surfaces on relatively wobbling rotating...
C403S370000, C403S368000, C403S374400
Reexamination Certificate
active
06227829
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns an eccentric screw pump having a pump shaft which at one end is in the form of a hollow shaft mounted near a joint head or the like connecting portion and connected thereto, and which is fitted on to the output shaft of a pump drive and is connected thereto.
The applicants DE 41 21 717 discloses an eccentric screw pump of that kind. Its pump connection shaft which is hollow towards its end is pushed on to the output shaft and connected thereto in positively locking relationship by a grooved dowel pin which crosses the shaft axis. The direct connection of the output shaft of the pump drive to the drive shaft of the pump, which is fitted on to same, can also be effected by spline connections.
For assembly and dismantling reasons those connections involve play and are protected from corrosion by additional sealing elements. In spite of that sealing effect and the use of anti-corrosion agents between the components it is not possible to exclude corrosion, in particular frictional or fretting corrosion or tribocorrosion.
In addition, by virtue of their design configuration, as a result of stress concentrations or notch effects which occur, those connections require large outside diameters for the pump shaft, with the consequence that they necessitate in particular shaft sealing components of greater size, in comparison with a pump without a push-on shaft connection, and that gives rise to an increased level of susceptibility on the part of such components.
SUMMARY OF THE INVENTION
In consideration of that state of the art the inventor set himself the aim, while retaining ease of assembly and dismantling, of avoiding the above-mentioned shaft play, corrosion and/or Lribocorrosion, as well as large outside pump shaft diameters and larger shaft sealing components.
That object is attained by the teaching set forth herein.
In accordance with the invention the output shaft is connected by a force-locking connection to the pump shaft which embraces it in the coupling region. For that purpose the pump shaft is at least partially in the form of a thin-walled hollow shaft without a notch-effect or stress-concentration transverse bore or spline or key groove and in accordance with a further feature of the invention it is clamped by a clamping device which produces radial forces and which is applied from the exterior on to the output shaft of the drive. With that arrangement torque and axial force transmission are effected by frictional engagement.
By virtue of those features the push-on shaft connection is radially and axially play-free and does not allow any relative movements. In addition this play-free, force-locking connection is pressure-tight. Corrosion and/or frictional or fretting corrosion are reliably prevented.
A further advantage that is to be seen therein is that the notch-free structure permits high loadings and thus small shaft diameters. As a result the outside diameter of the pump shaft is identical to those of existing pumps with continuous supported pump shaft and drive by way of a coupling means; in particular there is no need for relatively large shaft sealing components. When the clamping connection is released the hollow shaft springs open, which ensures easy dismantleability.
Advantageously the ratio of the wall thickness of the cylinder wall of the hollow shaft end to the shaft diameter is between 1:7 and 1:15, preferably being about 1:10.
In accordance with the invention the clamping device embraces the drive end of the pump shaft in the form of a hollow shaft, near the end edge of the cylinder wall in the region of a first bearing or support portion of a coupling end of the output shaft,
It has proven to be advantageous for the clamping device to have a clamping ring embracing the pump shaft, with an outside surface which is inclined at an angle towards the drive in relation to the longitudinal axis of the shaft, for an outside ring with a correspondingly inclined inside surface, and pulling or tension elements which are parallel to the axis and with which the clamping ring and the outside ring are displaceable towards each other in the axial direction; the outside ring is pulled towards the joint head into its clamping position.
In accordance with the invention the clamping ring is of an L-shaped configuration in cross-section and involves a pressure limb which bears at the inside against the pump shaft and on the other hand has the inclined outside surface, and a radial collar, wherein passing through the latter are clamping screws as the tension elements, which engage into the outside ring. The latter can be pulled towards the joint head by the clamping screws, whereby the radial pressure on the support portion embraced by the hollow end of the pump shaft increases.
Flexural moments—in particular increased flexural moments in the event of joint wear and thus increased loadings in relation to the hollow shaft and the clamping connection—are counteracted in accordance with the invention by the arrangement of a second bearing or support location between the joint engagement point and the clamping location or the first support portion.
To prevent tribocorrosion, an—annular—gap is advantageously arranged in the region between the two support locations or portions, the gap being delimited on the inward side by an intermediate portion of the coupling end and outwardly by the wall of the hollow end of the pump shaft.
REFERENCES:
patent: 2028407 (1936-01-01), Moineau
patent: 3957381 (1976-05-01), Schafer
patent: 4268185 (1981-05-01), Mullenberg
patent: 4471846 (1984-09-01), Mullenberg
patent: 5639176 (1997-06-01), Mullenberg
patent: 3410306 (1984-12-01), None
patent: 400508 (1933-10-01), None
patent: 622583 (1949-05-01), None
patent: 2163522 (1986-02-01), None
patent: 2244518 (1991-12-01), None
patent: 59-224489 (1984-12-01), None
Paul Alfred
Wehling Werner
Allweiler AG
Bachman & LaPointe P.C.
Denion Thomas
Trieu Theresa
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